You don't need too many dollars- we took 50% of anticipated spending which was too many. Agribank ATMs will allow you to draw 4, 000, 000 VND (about £120) for a 20,000 VND( 60p) fee-plus UK fee of course- other banks seemed to restrict the amounts to 2,000,000 for the same fee.
You don't need a sheet sleeping bag for the Mekong Delta, though I am not unhappy with the beautiful silk ones I bought for 75000 VND each.
Eating out etc is surprisingly cheap!
If you are thinking of tailor-made clothes take photos from home if you particularly like any designs- the tailors are expert in making them.
If you like milk in coffee you could consider taking some powdered milk since usually condensed milk is supplied.
July was very humid and hot especially in the north but we had far less rain than anticipated and simply jumped into taxis (also v cheap) if it poured. Personally I was not troubled at all by mosquitos though my husband would disagree!
We were fascinated by our visit to Ho Chi Minh's mausoleum, almost a pilgrimage for some Vietnamese and perhaps evidence of the influence of Communism, even today. This is not on the tour but well worth a visit.
We found the laundry services at the hotels quite expensive, plus some things stretched and others shrunk........you have been warned!